The present invention relates to an oscillating piston type compressor mainly used in an air conditioner or a refrigerating apparatus, and more particularly to an oscillating piston type compressor provided with a plate-shaped blade, which is projectingly formed integral with a cylindrical portion of a piston to partition a cylinder chamber into a suction chamber and a compression chamber and is shaped for efficient processing.
As disclosed in Japanese Patent Unexamined Publication No. 108445/1995, there has been known a double grinding processing method for grinding a workpiece by use of a pair of opposed grinding stones, as a technique for processing a pair of parallel surfaces. This processing method will now be described in details with reference to FIG. 12.
In FIG. 12, a carrier 60 for moving a workpiece passes between a pair of grinding stones 50a and 50b which rotate in opposite direction. In FIG. 12, the workpiece is a cylindrical ring 55. Before the carrier 60 enters between the grinding stones 50a and 50b, the ring 55 is inserted into an insertion portion 60a provided on the carrier 60 at, e.g., a point A, and the ring 55 passes between the grinding stones 50a and 50b with rotation of the carrier 60, thereby completing the processing. The ring 55 having been processed is ejected at, for example, a point B after the carrier 60 have passed between the grinding stones 50a and 50b. The double grinding processing method of the above constitution has a feature in that the both annular end surfaces of the ring 55 can be processed to a width defined by the grinding stones 50a and 50b to have favorable parallelism and flatness. This processing method has another feature in that parallel flat surfaces can be continuously ground in a short period of time, and the method has been used for processing end surfaces of a cylinder or side surfaces of a flat plate, as a technique for mass-production of parallel flat surfaces.
Further, Japanese Patent Unexamined Publication No. 247064/1996 discloses a configuration of a piston having a plate-shaped blade integrally formed on a cylindrical body, but a radial end of the blade is flat in conventional pistons.
In the case of using the above-described double grinding processing method to process side surfaces of a plate-shaped blade integrally formed on and projecting from a cylindrical portion of a piston, there are caused the following problems.
Matters taken account of in the prior art double grinding processing method are a width between and parallelism of two surfaces to be processed, and flatness and surface roughness of the respective surfaces. A workpiece is not constrained in the carrier in a direction, along which processing proceeds, and amounts of processing performed by the opposed two grinding stones are not forcedbly controlled.
Forces are applied on the workpiece to feed the same into a gap formed by the two grinding stones, and two surfaces of the workpiece are processed during movements of the workpiece. In this processing method, the gap between the grinding stones is controlled so as to obtain a desired width of the workpiece at the completion of processing. Accordingly, respective amounts of processing applied to the two surfaces to be processed vary depending on the nature of the grinding stones, but there is no means for individually controlling such amounts of processing.
As described above, since the prior art double processing method is not one, in which a workpiece is forcedly grasped by, e.g., a chuck, consideration is not commonly taken into to obtain accuracy of relative positions between the workpiece and other elements constituting members.
In the case where the double grinding processing is applied to blade side surfaces of a piston, it is difficult due to properties of such processing method to obtain accuracy of positional relationship between the blade side surfaces and a cylindrical portion. For example, this processing method has a difficulty in meeting a demand for carrying out processing in such a manner that a center line of the both blade side surfaces in a radial direction runs through a center of the cylindrical portion. More specifically, in the case where processing is to be controlled in such a manner that the center line of the both blade side surfaces in the radial direction runs through the center of the cylindrical portion, there is caused the need of changing amounts of processing on the respective blade side surfaces on the basis of the cylindrical portion. However, the conventional double grinding processing methods cannot control amounts of processing on the respective surfaces and so it is impossible to meet the above demand.
Also, with a blade of a prior art piston, a radial end portion of the blade is flat, so that when positioning is determined by grasping the blade, any portions except side surfaces of the blade being processed cannot determine positioning. Therefore, the blade of the prior art piston is configured such that when the blade side surfaces are processed, only the blade side surfaces themselves can be made a reference and constrained in position. That is, with a configuration of the conventional blade, it is difficult to process the blade side surfaces in a state, in which other portions than the blade side surfaces are constrained by a jig.
Therefore, when the blade side surfaces of the conventional piston are to be processed, it is common to perform processing in such a manner that one of the two blade side surfaces is used as a reference and the other of the blade side surfaces reserves machining allowance, to then invert the two blade side surfaces to further perform processing, and to repeat such work, in which processing is alternately applied to each blade side surface to obtain accuracy for a width dimension of the blade itself and a position of the blade with respect to the cylindrical portion, which makes a very inefficient operation.
In view of the above-described problems in the prior art, it is an object of the present invention to provide an oscillating piston type compressor provided with a piston, which is shaped to afford processing a blade by a double grinding method capable of efficient processing of parallel flat surfaces, and a method for processing the blade.
The present invention is achieved to attain the above object.
A first oscillating piston type compressor for attaining the above object comprises a cylinder having a hollow cylinder chamber; a piston formed integral with a plate-shaped blade, which is supported by the cylinder to be capable of rocking and radially sliding relative to the cylinder and partitions the cylinder chamber into a suction chamber and a compression chamber; a crankshaft inserted into the piston to cause the piston to make orbital motion in the cylinder chamber; and end plates supporting the crankshaft and closing both end openings of the cylinder, and a recess or a protrusion formed on a radial end surface of the blade of the piston to serve as a reference for positioning relative to an axis of the piston.
A second oscillating piston type compressor for attaining the above object has a feature in that in the first oscillating piston type compressor, the recess formed on the blade of the piston is a groove tapered to have a cross section in a direction perpendicular to the axis of the piston, decreasing in width toward the axis, and an extension of an axis of symmetry of the tapered portions runs substantially through a center of a cylindrical portion.
A third oscillating piston type compressor for attaining the above object has a feature in that in the first or second oscillating piston type compressor 1, a material for the piston is a sintered alloy adapted for molding with a die, and the recess or protrusion is molded with the die.
Also, a first method for attaining the above object is a method of processing side surfaces of a plate-shaped blade projectingly and integrally formed on a piston, the method comprising the steps of forming a recess or a protrusion, which makes a reference for positioning relative to an axis of the piston, on a radial end surface of the plate-shaped blade, and thereafter using two grinding stones with opposed annular grinding surfaces to perform grinding on two side surfaces of the blade in a state, in which an inside or outside diameter portion of the piston is supported and a support member is fitted into the reference from radially of the blade to support the same.
A second method for attaining the above object has a feature in that in the first method, after a gap defined between the two grinding stones is made larger than a width of the blade before double grinding, the blade is moved about processing portions of the two grinding stones and two side surfaces of the blade are processed while the gap between the two grinding stones is being decreased.
A third method for attaining the above object has a feature in that in the first or second method, an oblique angle is imparted to axes of rotation of the two grinding stones provided with opposed annular grinding surfaces, the grinding stones are configured to have portions in parallel to a median line of the oblique angle in a region where the gap between the two grinding stones becomes smallest, the grinding stones and the piston are arranged such that a center line of the gap defined between the two grinding stones formed in parallel to each other coincides with a line running through centers of a groove formed on the blade of the piston and a cylindrical portion of the piston, the blade of the piston is caused to reciprocate or pass repeatedly in one direction through the gap defined between the two grinding stones, and the blade is processed while the gap between the grinding stones is sequentially decreased.
A fourth method for attaining the above object has a feature in that in the first or second or third method, processing is performed by adding an oscillation motion, in which the blade of the piston is caused to reciprocate in a radial direction of the grinding stones arranged opposed to each other.
A fifth method for attaining the above object has a feature in that in the first or second or third or fourth method, a material for the piston is made from a sintered alloy adapted for molding with a die, the recess or protrusion serving as the reference is formed on a radial end surface of the blade upon molding with the die, and thereafter double grinding is applied on side surfaces of the blade.